After sexual exposure HIV crosses the mucosal barrier, establishes a nidus of infected cells which amplify the initial infectious inoculum and initiates subsequent systemic dissemination through the lymphatic and vascular systems. Several lines of evidence have indicated that chronic exposure to drugs of abuse is associated with an increased risk for the acquisition and faster progression of HIV infection. The large cohort of HIV-infected individuals who are recreational drug users and play a major role in disseminating infection must be effectively treated by any proposed regimen to reduce the spread of HIV infection. Design of effective treatments for this population would likely be enhanced by delineating the mechanisms by which substance increases the risk of HIV transmission and the impact of substance abuse on the efficacy of treatment. We hypothesize exposure to drugs of abuse such as opioid or amphetamine contributes to the increased rate of HIV infection in substance abusers by altering the lymphoid microenvironment to facilitate infection and replication of HIV in lymphoid tissues. A major barrier that impeded investigation of the early events of HIV infection, particularly the effect of substance abuse, is the lack of an animal model that is infectible by HIV. Recently, more robust humanized mouse models such as hu-NSG mice have been developed using highly immunodeficient mice transplanted with human hematopoietic stem cells. These mice display extensive engraftment of the mouse lymphoid tissues with human T cells, B cells, macrophages and dendritic cells enabling them to be infected with HIV by the intravenous, intraperitoneal, rectal or vaginal routes. We propose to combine this novel in vivo experimental model for investigating HIV transmission with a systems biology approach to analyze and characterize the effect of drugs of abuse on the initial and subsequent cellular targets of HIV infection during the establishment of HIV infection and generate microarray data sets to identify genes modulated by opioids or meth usage that contributes to their enhancement of the initiation and spread of HIV infection. Results from this proposed study will provide a multi-scale understanding of HIV infection in humanized mice using systems biology analysis of dedicated experiments and modeling that should permit us to develop a mechanistic and quantitative grasp of how HIV infection is initiated and spread in lymphoid tissues and how it is affected by substance abuse.